The broad, long-term objective of this application is to obtain a better understanding of the role of the lungs in a Plasmodium infection. The lungs contribute crucially to two stages of the disease. 1) Hepatic (first-generation) merozoites leave the liver as merosomes, large packets of parasites enclosed in hepatocyte membrane, and travel to the lungs where they are released into the blood. This critical transition between the silent liver phase and the symptomatic blood phase of the infection is completely unexplored. Because only a small number of hepatic merozoites are involved in this crucial segment of the life cycle, targeting this bottleneck may allow prevention of clinical malaria. 2) The subsequent generations of erythrocytic merozoites can sequester to the pulmonary microcirculation where they trigger inflammatory processes that damage endothelial cells leading to pulmonary edema due to breakdown of the blood-alveolar barrier. Acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), are important and frequently fatal complications in patients with severe malaria. The ability of infected red blood cells, leukocytes, and platelets to sequester within the pulmonary microcirculation has been demonstrated, predominantly in human autopsy material and to a certain degree also in a murine model of experimental severe malaria, but nothing is known about the dynamics of individual cellular interactions along the inflammatory cascade that ultimately leads to malarial ALI/ARDS. We plan to exploit the recent advances in intravital microscopic imaging, using transgenic parasites and mice in combination with highly specific fluorogenic reporter substrates and molecular probes, to address these important questions. Specific aims are to establish a murine model for intravital microscopy of the lungs, 2) define the dynamics of the cellular interactions associated with the pathogenesis of malarial ALI/ARDS, and 3) characterize the events associated with merosome arrest and merozoite release in the pulmonary microcirculation. Improved knowledge on parasite interaction with the lungs may help guide interventions to reduce the millions of annual deaths due to malaria, particularly in young children. PUBLIC HEALTH RELEVANCE: The lungs play a crucial role at two crucial stages of a malaria infection. This project aims to characterize dynamic cellular processes in the pulmonary microvasculature of Plasmodium-infected mice. A better understanding of the role of the lungs in a malaria infection may help design new approaches to reduce clinical symptoms in the 1 billion people that carry the parasite and to save the lives of the 2-3 million people, most of them children, who succumb to this devastating tropical disease every year.